Projector and lighting optical system therefor

ABSTRACT

The structure of the present invention makes dark lines due to a central axis of a cross dichroic prism sufficiently inconspicuous. A stepped reflecting mirror is interposed between a second lens array and a condenser. The stepped reflecting mirror has the function of deviating the optical path of part of the partial light fluxes among a plurality of partial light fluxes passing through a plurality of small lenses aligned on the same column in lens arrays from the optical path of the other partial light fluxes. A planar transparent member may be used in place of the stepped reflecting mirror for the purpose of deviating the optical path. Another technique shifts part of rows in the lens arrays and to deviate the optical path of part of the partial light fluxes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projection display apparatus withcolored light combining means and a lighting optical system therefor.

2. Discussion of the Background

A cross dichroic prism is often used for projection display apparatusthat project a color image on a projection screen. For example, in atransmissive liquid-crystal projector, the cross dichroic prism isutilized as colored light combining means that combines three coloredrays of red, green, and blue and emits the composite light in a commondirection. In a reflective liquid-crystal projector, the cross dichroicprism is utilized as colored light separation means that separated abeam of white light into three colored rays of red, green, and blue andalso as colored light combining means that recombines modulated threecolored rays and emits the composite light in a common direction. Aknown example of the projection display apparatus with the crossdichroic prism is disclosed in JAPANESE PATENT LAID-OPEN GAZETTE No.1-302385.

FIG. 17 conceptually illustrates a main part of a projection displayapparatus. The projection display apparatus includes threeliquid-crystal light valves 42, 44, and 46, a cross dichroic prism 48,and a projection lens system 50. The cross dichroic prism 48 combinesthree colored rays of red, green, and blue modulated by the threeliquid-crystal light valves 42, 44, and 46 and emits the composite lighttoward the projection lens system 50. The projection lens system 50focuses the composite light on a projection screen 52.

FIG. 18 is a partly decomposed perspective view illustrating the crossdichroic prism 48. The cross dichroic prism 48 includes four right-angleprisms which are bonded to one another via the respective right-anglesurfaces by an optical adhesive.

In the projection display apparatus using a cross dichroic prism as thecolored light combining means, according to the optical characteristicsof a light source applied, scattering of light at a joint of fourright-angle prisms may cause a dark shadow on a projected image.

FIG. 19 shows a problem arising in the case of utilizing the crossdichroic prism 48. As shown in FIG. 19(A), the cross dichroic prism 48has a red light reflection film 60R and a blue light reflection film 60Bwhich are arranged in a substantially X shape on an X-shaped interfaceformed by the right-angle surfaces of the four right-angle prisms. Thereis a layer of optical adhesive 62 formed in the gaps between the fourright-angle prisms. Both the reflection films 60R and 60B accordinglyhave gaps at a central axis 48a of the cross dichroic prism 48.

When a light beam passing through the central axis 48a of the crossdichroic prism 48 is projected on the projection screen 52, a dark linedue to the central axis 48a may be formed in the projected image. FIG.19(B) shows an example of the dark line DL. The dark line DL representsa relatively dark, linear area having a different color from that of theother part and is formed substantially on the center of the projectedimage. It is considered that the dark line DL is ascribed to scatteringof rays and no-reflection of the red light and blue light in the gaps ofthe reflection films in the vicinity of the central axis 48a. A similarproblem arises in a cross dichroic mirror that includes two dichroicmirrors that are arranged in an X shape and respectively have selectivereflection films, such as a red reflection film and a blue reflectionfilm. In this case, a dark line due to a central axis of the mirror isformed in a projected image.

As described above, in the prior-art projection display apparatus, adark line is formed substantially on the center of a projected imagebecause of the central axis of the cross dichroic prism 48 or the crossdichroic mirror.

SUMMARY OF THE INVENTION

In order to solve the above problem in the prior art, one object of thepresent invention is to provide a technique that makes a dark line dueto a central axis of colored light combining means inconspicuous, wherethe colored light combining means includes two dichroic films arrangedsubstantially in an X shape and may be a cross dichroic prism or a crossdichroic mirror. Another object of the present invention is to realize alighting optical system and a projection display apparatus based on thistechnique.

The principle for solving the problem is described first with a concreteexample shown in FIGS. 1 through 4. In the drawings, z direction denotesdirection of the course of light, x direction denotes the direction of 3o'clock seen from the direction of the course of light (the zdirection), and y direction denotes the direction of 12 o'clock. In thedescription below, the x direction represents the direction of rows andthe y direction represents the direction of columns for the matter ofconvenience. Although the description of the principle is based on aconcrete example for the better understanding, the present invention isnot restricted to this concrete structure in any sense.

In a projection display apparatus, a lighting optical system with twolens arrays each including a plurality of small lenses (hereinafterreferred to as an integrator optical system) as specified in WO94/22042is known as the technique for dividing light from a light source into aplurality of partial light fluxes and thereby reducing an in-planeunevenness of the illuminance of light.

FIG. 1 shows the principle of forming a dark line when an integratoroptical system is adopted in a projection display apparatus with a crossdichroic prism. FIGS. 1(A-1) and 1(B-1) show light fluxes (shown by thesolid lines) passing through a plurality of small lenses 10 which aredifferent in position in the x direction, that is, a plurality of smalllenses 10 existing in different columns, and traces of their centraloptical axes (shown by the fine dotted lines). FIGS. 1(A-2) and 1(B-2)show the positions of dark lines DLa and DLb formed on a projectionscreen 7.

A light flux emitted from a light source (not shown) is divided into aplurality of partial light fluxes by first and second lens arrays 1 and2 each including the plurality of small lenses 10. The light fluxespassing through the respective small lenses 10 included in the first andthe second lens arrays 1 and 2 are converted to light fluxes parallel tothe respective central axes of the light fluxes by means of aparalleling lens 15. The light fluxes passing through the parallelinglens 15 are superposed on a liquid-crystal light valve 3, so that apredetermined area is uniformly illuminated with the superposed lightfluxes. Although only one liquid-crystal light valve 3 is shown in FIG.1, the principle of the integrator optical system and the principle offorming a dark line are also applicable to the other two liquid-crystallight valves.

FIG. 2 is a perspective view illustrating the appearance of the lensarrays 1 and 2. Each of the first and the second lens arrays 1 and 2includes the small lenses 10 that respectively have a substantiallyrectangular outline and are arranged in a matrix of M rows and Ncolumns. In this example, M=10 and N=8. FIG. 1(A-1) shows the trace ofpartial light fluxes passing through the small lenses 10 of the secondcolumn, whereas FIG. 1(B-1) shows the trace of partial light fluxespassing through the small lenses 10 of the seventh column.

The light fluxes superposed on the liquid-crystal light valve 3 aresubjected to modulation responsive to image information in theliquid-crystal light valve 3 and enter a cross dichroic prism 4. Thelight flux output from the cross dichroic prism 4 is projected on theprojection screen 7 via a projection lens system 6.

As shown by the rough dotted lines in FIGS. 1(A-1) and 1(B-1), lightfluxes passing through a central axis 5 (along the y direction in thedrawing) of the cross dichroic prism 4 are projected at positions Pa andPb on the projection screen 7. As discussed previously as the problemaddressed by the invention, scattering of the rays and no-reflection ofthe light to be reflected in the gaps between reflection films in thevicinity of the central axis 5 reduce the quantity of light passingthrough the vicinity of the central axis 5. As shown in FIGS. 1(A-2) and1(B-2), the reduction causes dark lines DLa and DLb, which have thelower luminance than the area around on the projection screen 7.

The dark line has the following relation to the first and the secondlens arrays 1 and 2. As clearly shown in FIG. 3(A), which is a partialenlarged view of FIG. 1(A-1), the image formed by the liquid-crystallight valve 3 is inverted and magnified by the projection lens system 6and projected on the projection screen 7. FIG. 3(B) is a cross sectionalview showing an x-y plane including the central axis 5 of the crossdichroic prism 4. Referring to FIGS. 3(A) and 3(B), in case that apartial light flux is cut by the x-y plane including the central axis 5of the cross dichroic prism 4, r1 denotes a distance from one end 11 ofa cross section 8 of the partial light flux to the central axis 5, andr2 denotes a distance from the other end 12 of the cross section 8 ofthe partial light flux to the central axis 5. The image of the crosssection 8 of the partial light flux is inverted and magnified by theprojection lens system 6 and projected on the projection screen 7. Aratio of a distance R2 from one end 13 of a projection area 9 on theprojection screen 7 to the dark line DLa to a distance R1 from the otherend 14 of the projection area 9 to the dark line DLa is accordinglyequal to the ratio of r2 to r1. In other words, the position where thedark line DLa is formed depends upon the position where the crosssection 8 of the partial light flux exists relative to the central axis5 in the x-y plane including the central axis 5 of the cross dichroicprism 4.

In the examples of FIGS. 1(A-l) and 1(B-1), the partial light fluxeshave cross sections at different positions in the x-y plane includingthe central axis 5 of the cross dichroic prism 4. This means that thedark lines DLa and DLb are formed at different positions. In a similarmanner, the partial light fluxes passing through the small lenses 10existing in the columns other than the second column and the seventhcolumn in the first and the second lens arrays 1 and 2 have crosssections at different positions in the x-y plane including the centralaxis 5 of the cross dichroic prism 4. A number of dark linescorresponding to the number of columns included in the first and thesecond lens arrays 1 and 2, N dark lines in this example, are thusformed on the projection screen 7.

The partial light fluxes passing through the M small lenses aligned onthe same column in the first and the second lens arrays 1 and 2 formdark lines DLc at approximately the same position on the projectionscreen 7 as shown in FIG. 4. Each of the N dark lines is formed bysuperposing the partial light fluxes passing through the M small lensesaligned on the same column in the first and the second lens arrays 1 and2. The degree of darkness of each dark line is substantially identicalwith the summation of the degree of darkness of the dark lines formed bythe respective small lenses.

The above description leads to the following principles.

First Principle

The first principle is that the different positions of the centraloptical paths of the partial light fluxes relative to the central axis 5of the cross dichroic prism 4 cause dark lines to be formed at differentpositions. The partial light fluxes passing through the differentcolumns included in the first and the second lens arrays 1 and 2 aredifferent in position relative to the central axis 5 of the crossdichroic prism 4 and thereby form dark lines at different positions.

Second Principle

The second principle is that the different positions of the crosssections of the partial light fluxes in the x-y plane including thecentral axis 5 of the cross dichroic prism 4 are ascribed to thedifference in incident angles of the partial light fluxes entering thecross dichroic prism 4 (see FIG. 1). The partial light fluxes passingthrough the different columns included in the first and the second lensarrays 1 and 2 enter the cross dichroic prism 4 at different incidentangles and thereby have cross sections at different positions relativeto the central axis 5.

Namely different incident angles of the partial light fluxes enteringthe cross dichroic prism 4 or different angles of the partial lightfluxes superposed on the liquid-crystal light valve 3 cause dark linesto be formed at different positions.

Method of Making Dark Lines Inconspicuous

As discussed previously, the partial light fluxes passing through the Msmall lenses aligned on the same column in the first and the second lensarrays 1 and 2 respectively form dark lines at substantially the sameposition on the projection screen 7. The degree of darkness of eachresulting dark line is substantially equal to the summation of thedegree of darkness of the dark lines formed by the respective smalllenses. A desired arrangement accordingly causes dark lines to be formedat different positions on the projection screen 7 by the respectivepartial light fluxes passing through the M small lenses. Althoughincreasing the total number of dark lines, this arrangement decreasesthe degree of darkness per each dark line, thereby making each dark linesufficiently inconspicuous. It is, however, not required to cause allthe dark lines to be formed at different positions by the respectivepartial light fluxes passing through the M small lenses. One preferableapplication accordingly causes only part of the dark lines to be formedat different positions.

Formation of dark lines at different positions is realized according tothe first principle and the second principle discussed above.

Based on the first principle, as for part of the partial light fluxespassing through the M small lenses arranged on the same direction ofcolumns, the positions of the central axes of the partial light fluxesrelative to the central axis 5 of the cross dichroic prism 4 should bechanged from the others.

Based on the second principle, as for part of the partial light fluxespassing through the M small lenses arranged on the same direction ofcolumns, the angles of the partial light fluxes superposed on theliquid-crystal light valve 3 or the incident angles of the partial lightfluxes entering the cross dichroic prism 4 should be changed from theothers.

The present invention has solved the problem of the prior art discussedpreviously according to the above principles. The following describesthe means for solving the problem and its functions and effects.

Means for Solving the Problems and its Functions and Effects

A first projection display apparatus is a projection display apparatuscomprising: a lighting optical system which emits light; colored lightseparation means which separates the light into three colored rays;three light modulation means which respectively modulate the threecolored rays based on given image signals; colored light combining meanswhich has two dichroic films arranged in an X shape and a central axiscorresponding to a position where the two dichroic films cross eachother, the colored light combining means combining the three coloredrays respectively modulated by the three light modulation means tocomposite light and outputting the composite light in a commondirection; and projection means which projects the composite lightoutput from the colored light combining means on a projection surface,wherein the lighting optical system comprises a dividing and superposingoptical system that divides a light flux into a plurality of partiallight fluxes, which are arranged in a direction of columns substantiallyparallel to the central axis of the colored light combining means and ina direction of rows substantially perpendicular to the central axis ofthe colored light combining means, and superposes the plurality ofpartial light fluxes, and wherein the dividing and superposing opticalsystem is constructed to shift a position where the central axis isprojected on the projection surface by part of the partial light fluxesamong the partial light fluxes on an identical column from a positionwhere the central axis is projected by the other partial light fluxes onthe identical column, the positional shift being in a directiondifferent from a direction corresponding to the central axis.

One partial light flux projects the central axis of the colored lightcombining means on the projection surface to form a dark linecorresponding to the central axis. A plurality of partial light fluxesaligned on one column generally project the central axis of the coloredlight combining means at substantially the same position on theprojection surface to form a dark line. The arrangement of the presentinvention causes part of the partial light fluxes among the plurality ofthe partial light fluxes on one column to project the central axis ofthe colored light combining means as a dark line at a different positionon the projection surface from the position of the central axisprojected by the other partial light fluxes. This structure makes thedark lines formed on the projected image sufficiently inconspicuous.

In accordance with one preferred arrangement of the first projectiondisplay apparatus, the dividing and superposing optical systemcomprises: light flux dividing means which divides the light flux intothe plurality of partial light fluxes; and incident angle changing meansthat causes the part of the partial light fluxes among the partial lightfluxes on the identical column to enter the colored light combiningmeans at an incident angle different from that of the other partiallight fluxes.

It is further preferable that the light flux dividing means has at leastone lens array having a plurality of small lenses arranged in thedirections of columns and rows, and the incident angle changing meanshas a stepped reflecting mirror having a step part on a reflectingsurface thereof.

In another example, it is also preferable that the light flux dividingmeans has at least one lens array having a plurality of small lensesarranged in the directions of columns and rows, and the incident anglechanging means has a transparent member arranged to be inclined relativeto a surface of the lens array.

This preferable arrangement enables the position of the central opticalpath of the part of the partial light fluxes relative to the centralaxis of the colored light combining means to be deviated from theposition of the central optical path of the other partial light fluxes.The part of the partial light fluxes and the other partial light fluxesaccordingly form dark lines at different positions. This makes the darklines formed on the projected image sufficiently inconspicuous. Eitherone of the above combinations makes the dark lines formed on theprojected image more inconspicuous.

A second projection display apparatus is a projection display apparatuscomprising: a lighting optical system which emits light; colored lightseparation means which separates the light into three colored rays;three light modulation means which respectively modulate the threecolored rays based on given image signals; colored light combining meanswhich has two dichroic films arranged in an X shape and a central axiscorresponding to a position where the two dichroic films cross eachother, the colored light combining means combining the three coloredrays respectively modulated by the three light modulation means tocomposite light and outputting the composite light in a commondirection; and projection means which projects the composite lightoutput from the colored light combining means on a projection surface,wherein the lighting optical system comprises: a first lens array havinga plurality of small lenses that divide a light flux emitted from alight source into a plurality of partial light fluxes; a second lensarray having a plurality of small lenses that respectively correspond tothe plurality of small lenses of the first lens array; and optical pathshifting means which shifts an optical path of part of the partial lightfluxes among a plurality of partial light fluxes passing through theplurality of small lenses arranged in a predetermined directioncorresponding to the central axis of the colored light combining meansfrom an optical path of the other partial light fluxes among theplurality of partial light fluxes.

A plurality of partial light fluxes passing through the small lensesaligned in a predetermined direction corresponding to the central axisof the colored light combining means among the plurality of small lensesin the first and the second lens arrays project the central axis of thecolored light combining means at substantially the same position on theprojection surface to form a dark line. The optical path shifting meansshifts the optical path of part of the partial light fluxes among theplurality of partial light fluxes from the optical path of the otherpartial light fluxes. Based on the first principle discussed above, thisarrangement prevents the plurality of partial light fluxes fromprojecting the central axis of the colored light combining means atsubstantially the same position, thereby making the dark lines formed onthe projected image sufficiently inconspicuous.

In accordance with one preferable arrangement of the second projectiondisplay apparatus, the optical path shifting means comprises means whichshifts the optical path of the partial light fluxes passing throughpositions respectively apart from an optical axis of the light source bya specified distance in the predetermined direction from the opticalpath of the partial light fluxes passing through the other positions.

The intensity of light from the light source depends upon the distanceapart from the optical axis of the light source. Shifting the opticalpath of the partial light fluxes having the relatively high intensity oflight from the optical path of the other partial light fluxes makes thedark lines formed on the projected image sufficiently inconspicuous.

In case that the light source includes a light-source lamp and a concavemirror that reflects light emitted from the light-source lamp, it ispreferable that the specified distance is substantially equal to a focaldistance of the concave mirror. The partial light fluxes passing throughthe positions respectively apart from the optical axis of the lightsource by the focal distance of the concave mirror have the higherintensity of light than those of the other partial light fluxes.Shifting the optical path of the partial light fluxes passing throughthese specified positions from the optical path of the other partiallight fluxes passing through the other positions makes the dark linesformed on the projected image sufficiently inconspicuous.

In accordance with another preferable arrangement of the secondprojection display apparatus, the optical path shifting means has astepped reflecting mirror having a step part on a reflecting surfacethereof. This simple arrangement can arbitrarily change the optical pathof specified partial light fluxes.

It is preferable that the step part of the stepped reflecting mirror isarranged to extend in a direction perpendicular to the directioncorresponding to the central axis of the colored light combining means.This arrangement enables the optical path of part of the partial lightfluxes to be shifted in the direction corresponding to the central axisof the colored light combining means.

It is also preferable that the stepped reflecting mirror has a firstreflecting surface and a second reflecting surface of different heights,the second reflecting surface being arranged at two different positionsrespectively apart from an optical axis of the light source by aspecified distance in the predetermined direction corresponding to thecentral axis of the colored light combining means. The two secondreflecting surfaces respectively change the optical path of the partiallight fluxes having the relatively high intensity of light.

In another embodiment, the optical path shifting means may comprise atransparent member arranged to be inclined relative to a surface of thesecond lens array. This arrangement can arbitrarily change the opticalpath of specified partial light fluxes.

In accordance with one preferable arrangement, the lighting opticalsystem further comprises: a polarizing element disposed at a positionbetween the second lens array and the optical path shifting means,wherein the polarizing element comprises: a polarization beam splitterarray which has plural sets of a polarization separating film and areflecting film that are parallel to each other, the polarization beamsplitter array separating each of the plurality of partial light fluxespassing through the plurality of small lenses of the second lens arrayinto two types of linear polarized light components; and a polarizerwhich equalizes polarizing directions of the two types of linearpolarized light components separated by the polarization beam splitterarray, and wherein the optical path shifting means shifts part ofoptical paths of the two types of linear polarized light components,which pass through the plurality of small lenses arranged in thepredetermined direction corresponding to the central axis of the coloredlight combining means and are separated by the polarization beamsplitter array, from the other optical paths.

In the polarizing element, after the polarization beam splitter arrayseparates the incident light into two types of linear polarized lightcomponents, the polarizer equalizes the polarizing directions of thesetwo types of linear polarized light components. Shifting part of opticalpaths of the two types of linear polarized light component separated bythe polarization beam splitter array from the other optical paths makesthe dark lines formed on the projected image more inconspicuous.

It is preferable that an amount of shift by which the part of theoptical paths of the two types of linear polarized light components areshifted from the other optical paths by the optical path shifting meansis approximately half a distance between adjoining optical paths of thetwo types of linear polarized light components.

Shifting the optical path by approximately half the distance between theadjoining optical paths of the two types of linear polarized lightcomponents enables the optical paths of the shifted two types of linearpolarized light components and those of the non-shifted two types oflinear polarized light components to be arranged at substantially equalintervals. The arrangement of the four optical paths at substantiallyequal intervals makes the dark lines formed on the projected image mostinconspicuous.

In accordance with another arrangement, the second projection displayapparatus further comprises: a superposing optical system whichsuperposes a plurality of partial light fluxes passing through the firstlens array and the second lens array to illuminate the three lightmodulation means, wherein the optical path shifting means is disposedbetween the second lens array and the superposing optical system.

A third projection display apparatus is a projection display apparatuscomprising: a lighting optical system which emits light; colored lightseparation means which separates the light into three colored rays;three light modulation means which respectively modulate the threecolored rays based on given image signals; colored light combining meanswhich has two dichroic films arranged in an X shape and a central axiscorresponding to a position where the two dichroic films cross eachother, the colored light combining means combining the three coloredrays respectively modulated by the three light modulation means tocomposite light and outputting the composite light in a commondirection; and projection means which projects the composite lightoutput from the colored light combining means on a projection surface,wherein the lighting optical system comprises: a first lens array havinga plurality of small lenses that divide a light flux emitted from alight source into a plurality of partial light fluxes; and a second lensarray having a plurality of small lenses that respectively correspond tothe plurality of small lenses of the first lens array, each of the firstlens array and the second lens array being divided in a direction ofrows perpendicular to a direction corresponding to the central axis ofthe colored light combining means into a plurality of rows each having aplurality of small lenses, wherein rows located respectively apart froman optical path of the light source by a specified distance in thedirection corresponding to the central axis of the colored lightcombining means are arranged at positions shifted from the other rows bya fixed amount of shift.

A plurality of partial light fluxes passing through the small lensesaligned in a predetermined direction corresponding to the central axisof the colored light combining means among the plurality of small lensesin the first and the second lens arrays project the central axis of thecolored light combining means at substantially the same position on theprojection surface to form a dark line. In case that the light sourceincludes a light-source lamp and a concave mirror that reflects lightemitted from the light-source lamp, the partial light fluxes passingthrough the small lenses on specific rows existing at the positionsrespectively apart from the optical axis of the light source by thefocal distance of the concave mirror have the relatively high intensityof light. Based on the second principle discussed above, shifting thesespecific rows from the other rows makes the dark lines formed on theprojected image sufficiently inconspicuous.

A fourth projection display apparatus is a projection displaycomprising: a lighting optical system which emits light; colored lightseparation means which separates the light into three colored rays;three light modulation means which respectively modulate the threecolored rays based on given image signals; colored light combining meanswhich has two dichroic films arranged in an X shape and a central axiscorresponding to a position where the two dichroic films cross eachother, the colored light combining means combining the three coloredrays respectively modulated by the three light modulation means tocomposite light and outputting the composite light in a commondirection; and projection means which projects the composite lightoutput from the colored light combining means on a projection surface,wherein the lighting optical system comprises: a first lens array havinga plurality of small lenses that divide a light flux emitted from alight source into a plurality of partial light fluxes; and a second lensarray having a plurality of small lenses that respectively correspond tothe plurality of small lenses of the first lens array, each of the firstlens array and the second lens array being divided in a direction ofrows perpendicular to a direction corresponding to the central axis ofthe colored light combining means into a plurality of rows each having aplurality of small lenses, wherein at least part of the rows among theplurality of rows are arranged at a position shifted from the otherrows, and a number of rows whose small lenses are arranged at identicalpositions in a direction perpendicular to the direction of rows is setto be not greater than two fifths of a total number of the plurality ofrows.

A plurality of partial light fluxes passing through the small lensesaligned in a predetermined direction corresponding to the central axisof the colored light combining means among the plurality of small lensesin the first and the second lens arrays project the central axis of thecolored light combining means at substantially the same position on theprojection surface to form a dark line. In the fourth projection displayapparatus, the number of rows arranged at the equivalent positions isreduced to be not greater than two fifths of the total number of rows.Based on the second principle discussed above, this structure makes thedark lines formed on the projected image sufficiently inconspicuous.

In accordance with one preferable arrangement of the fourth projectiondisplay apparatus, the plurality of rows in the first lens array and thesecond lens array are shifted from one another by a fixed amount ofshift.

This arrangement readily reduces the number of rows arranged at theequivalent positions.

A first lighting optical system is a lighting optical system foremitting light for use in a projection display apparatus comprising:colored light separation means which separates the light into threecolored rays; three light modulation means which respectively modulatethe three colored rays based on given image signals; colored lightcombining means which has two dichroic films arranged in an X shape anda central axis corresponding to a position where the two dichroic filmscross each other, the colored light combining means combining the threecolored rays respectively modulated by the three light modulation meansto composite light and outputting the composite light in a commondirection; and projection means which projects the composite lightoutput from the colored light combining means on a projection surface,the lighting optical system comprising: a dividing and superposingoptical system that divides a light flux into a plurality of partiallight fluxes, which are arranged in a direction of columns substantiallyparallel to the central axis of the colored light combining means and ina direction of rows substantially perpendicular to the central axis ofthe colored light combining means, and superposes the plurality ofpartial light fluxes, wherein the dividing and superposing opticalsystem is constructed to shift a position where the central axis isprojected on the projection surface by part of the partial light fluxesamong the partial light fluxes on an identical column from a positionwhere the central axis is projected by the other partial light fluxes onthe identical column, the positional shift being in a directiondifferent from a direction corresponding to the central axis.

A second lighting optical system is a lighting optical system foremitting light comprising: a first lens array having a plurality ofsmall lenses that divide a light flux emitted from a light source into aplurality of partial light fluxes; a second lens array having aplurality of small lenses that respectively correspond to the pluralityof small lenses of the first lens array; and optical path shifting meanswhich shifts an optical path of part of the partial light fluxes among aplurality of partial light fluxes passing through the plurality of smalllenses arranged in a predetermined direction from an optical path of theother partial light fluxes among the plurality of partial light fluxes.

A third lighting optical system is a lighting optical system foremitting light comprising: a first lens array having a plurality ofsmall lenses that divide a light flux emitted from a light source into aplurality of partial light fluxes; and a second lens array having aplurality of small lenses that respectively correspond to the pluralityof small lenses of the first lens array, each of the first lens arrayand the second lens array are divided in a direction of rowsperpendicular to a predetermined direction into a plurality of rows eachhaving a plurality of small lenses, wherein rows located respectivelyapart from an optical path of the light source by a specified distancein the predetermined direction are arranged at positions shifted fromthe other rows by a fixed amount of shift.

A fourth lighting optical system is a lighting optical system foremitting light comprising: a first lens array having a plurality ofsmall lenses that divide a light flux emitted from a light source into aplurality of partial light fluxes; and a second lens array having aplurality of small lenses that respectively correspond to the pluralityof small lenses of the first lens array, each of the first lens arrayand the second lens array are divided in a direction of rowsperpendicular to a predetermined direction into a plurality of rows eachhaving a plurality of small lenses, wherein at least part of the rowsamong the plurality of rows are arranged at a position shifted from theother rows, and a number of rows whose small lenses are arranged atidentical positions in a direction perpendicular to the direction ofrows is set to be not greater than two fifths of a total number of theplurality of rows.

The `predetermined direction` in the second through the fourth lightingoptical systems corresponds to that of the central axis of the coloredlight combining means in the projection display apparatus. The directionof rows is accordingly perpendicular to that of the central axis.

Like the first through the fourth projection display apparatuses,application of any one of the first through the fourth lighting opticalsystems to the projection display apparatus makes the dark lines formedon the projected image sufficiently inconspicuous.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the principle of forming a dark line when an integratoroptical system is adopted in a projection display apparatus with a crossdichroic prism;

FIG. 2 is a perspective view illustrating the appearance of two lensarrays 1 and 2;

FIG. 3(A) is a partial enlarged view of FIG. 1(A-1) and FIG. 3(B) across sectional view showing an x-y plane including a central axis 5 ofa cross dichroic prism 4;

FIG. 4 conceptually shows the state in which the partial light fluxeswhich have passed through small lenses aligned on an N-th column in thetwo lens arrays 1 and 2 are projected on a projection screen 7;

FIG. 5 is a plan view schematically illustrating a main part of aprojection display apparatus 1000 as a first embodiment according to thepresent invention;

FIG. 6 is a perspective view illustrating the appearance of a first anda second lens arrays 120 and 130;

FIGS. 7(A), 7(B) show a structure of a polarizing element 140;

FIGS. 8(A), 8(B), 8(C) are plan views showing a structure of a steppedreflecting mirror 150 in the first embodiment;

FIG. 9 shows the function of the stepped reflecting mirror 150;

FIG. 10 shows the function of the stepped reflecting mirror 150;

FIG. 11 is an enlarged view illustrating part of the stepped reflectingmirror 150 and the polarizing element 140 of FIG. 9;

FIG. 12 illustrates a main part of a projection display apparatus 2000and its lighting optical system as a second embodiment according to thepresent invention;

FIGS. 13(A) and 13(B) are front views showing the comparison between thelens arrays used in the first embodiment and in a third embodiment;

FIG. 14 shows the state in which partial light fluxes passing throughthe small lenses are transmitted by a cross dichroic prism 260;

FIGS. 15(A), 15(B), 15(C) and 15(D) show the comparison between thepolarizing elements used in the first embodiment and the thirdembodiment;

FIGS. 16(A) and 16(B) are front views showing the comparison between thelens arrays used in the first embodiment and in a fourth embodiment;

FIG. 17 conceptually illustrates a main part of a projection displayapparatus;

FIG. 18 is a partly decomposed perspective view illustrating a crossdichroic prism 48; and

FIGS. 19(A) and 19(B) show a problem arising in the case of utilizingthe cross dichroic prism 48.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following describes some embodiments of the present invention byreferring to the drawings. In the respective embodiments discussedbelow, z direction denotes the direction of the course of light, xdirection denotes the direction of 3 o'clock seen from the z direction,and y direction denotes the direction of 12 o'clock, unless otherwisespecified.

A. First Embodiment

FIG. 5 is a plan view schematically illustrating a main part of aprojection display apparatus 1000 as a first embodiment according to thepresent invention. The projection display apparatus 1000 includes: alighting optical system 100; dichroic mirrors 210 and 212; reflectingmirrors 220, 222, and 224; an entrance lens 230; a relay lens 232; threefield lenses 240, 242, and 244; three liquid-crystal light valves(liquid-crystal panels) 250, 252, and 254; a cross dichroic prism 260;and a projection lens system 270.

The lighting optical system 100 includes: a light source 110 that emitsa substantially parallel light flux; a first lens array 120; a secondlens array 130; a polarizing element 140 which converts the incidentlight to a predetermined linear polarized light component; a steppedreflecting mirror 150; and a superposing lens 160. The lighting opticalsystem 100 is an optical system that substantially uniformly illuminatesthe three liquid-crystal light valves 250, 252, and 254.

The light source 110 has a light-source lamp 112 used as a radiant lightsource for emitting a radiant ray of light and a concave mirror 114 forconverting the radiant ray of light emitted from the light-source lamp112 to a substantially parallel light flux. One preferable example ofthe concave mirror 114 is a parabolic reflector.

FIG. 6 is a perspective view illustrating the appearance of the firstand the second lens arrays 120 and 130. The first lens array 120includes small lenses 122 which respectively have a substantiallyrectangular shape and are arranged in a matrix of M rows and N columns.In this example, M=10 and N=8. The second lens array 130 also includessmall lenses that are arranged in a matrix of M rows and N columnscorresponding to the small lenses 122 of the first lens array 120. Thesmall lenses 122 divide the light flux emitted from the light source 110(FIG. 5) into a plurality of (that is, M×N) partial light fluxes andcondense the respective partial light fluxes in the vicinity of thesecond lens array 130. The contour of each small lens 122 seen from thedirection z is set to be substantially similar to the shape of theliquid-crystal light valves 250, 252, and 254. In this embodiment, theaspect ratio (the ratio of the lateral dimension to the verticaldimension) of each small lens 122 is set equal to 4 to 3.

The second lens array 130 has the function of making the central opticalpaths of the respective partial light fluxes parallel to the systemoptical axis. When the light flux emitted from the light source 110 isparallel to the system optical axis, the partial light fluxes outputfrom the small lenses 122 of the first lens array 120 have centraloptical paths parallel to the system optical axis, so that the secondlens array 130 may be omitted. When the central optical path of thelight emitted from the light source 110 has a certain angle with respectto the system optical axis, however, the central optical paths of thepartial light fluxes output from the small lenses 122 are not parallelto the system optical axis. The partial light fluxes having suchinclined central optical paths may not illuminate a predetermined targetarea, that is, target areas on the liquid-crystal light valves 250, 252,and 254. This lowers the utilization efficiency of light in theprojection display apparatus. The second lens array 130 converts thepartial light fluxes having central optical paths that is inclined tothe system optical axis and entering the respective small lenses 132 tothe partial light fluxes having central optical paths parallel to thesystem optical axis, thereby improving the utilization efficiency oflight.

FIG. 7 illustrates structure of the polarizing element 140 (FIG. 5). Thepolarizing element 140 includes a polarization beam splitter array 141and a selective phase difference plate 142. The polarization beamsplitter array 141 includes a plurality of columnar transparent members143 having a parallelogrammatic cross section, which are bonded to oneanother. Polarization separating films 144 and reflecting films 145 areformed alternately on the interfaces of the transparent members 143. Inorder to enable the polarization separating film 144 and the reflectingfilm 145 to be arranged alternately, the polarization beam splitterarray 141 is manufactured by bonding a plurality of sheet glasses withthese films formed thereon and cutting the bonded sheet glasses slantlyat a predetermined angle.

The light of random polarizing directions passing through the first andthe second lens arrays 120 and 130 is separated by the polarizationseparating film 144 into s-polarized light and p-polarized light. Thes-polarized light is reflected from the polarization separating film 144substantially at a right angle and further from the reflecting film 145perpendicularly, whereas the p-polarized light passes through thepolarization separating film 144. The selective phase difference plate142 is an optical element having λ/2 phase difference layers 146disposed on the light-exit surfaces of the light passing through thepolarization separating films 144. There are no λ/2 phase differencelayers on the light-exit surfaces of the light reflected from thereflecting films 145. The λ/2 phase difference layer 146 accordinglyconverts the p-polarized light transmitted by the polarizationseparating film 144 to s-polarized light. As a result, the light fluxesof random polarizing directions entering the polarizing element 140 aremostly converted to s-polarized light.

As clearly shown in FIG. 7(A), the position of the center of thes-polarized light emitted from one polarization separating film 144 ofthe polarizing element 140 (that is, the position of the center when thetwo rays of s-polarized light are regarded as one set of light flux) isdeviated in the x direction from the center of the incident random lightflux (s-polarized light+p-polarized light). The shift is equal to half awidth Wp of the λ/2 phase difference layer 146 (that is, half the widthof the polarization separating film 144 in the x direction). As shown inFIG. 5, the optical axis of the light source 110 (shown by the two-dotchain line) is accordingly shifted from the system optical axis (shownby the one-dot chain line) after the polarizing element 140 by adistance equal to Wp/2.

In the projection display apparatus shown in FIG. 5, the parallel lightflux emitted from the light source 110 is divided into a plurality ofpartial light fluxes by the first and the second lens arrays 120 and 130in the integrator optical system. The small lenses 122 of the first lensarray 120 condense the respective partial light fluxes in the vicinityof the polarization separating films 144 of the polarizing element 140(see FIG. 7). The partial light fluxes output from the polarizingelement 140 are reflected from the stepped reflecting mirror 150. Thestructure and function of the stepped reflecting mirror 150 will bedescribed later. The superposing lens 160 has the function of thesuperposing optical system that superposes and condenses the pluralityof partial light fluxes on the liquid-crystal light valves 250, 252, and254, that is, on the areas to be illuminated. This enables therespective liquid-crystal light valves 250, 252, and 254 to beilluminated in a substantially uniform manner.

The two dichroic mirrors 210 and 212 have the function of the coloredlight separation means that separates a ray of white light condensed bythe superposing lens 160 into three colored rays of red, green, andblue. The first dichroic mirror 210 transmits a red light component ofthe white light flux emitted from the lighting optical system 100, whilereflecting a blue light component and a green light component. The redlight transmitted by the first dichroic mirror 210 is reflected from thereflecting mirror 220, passes through the field lens 240, and eventuallyreaches the liquid-crystal light valve 250 for red light. The field lens240 has the function of converting the partial light fluxes output fromthe polarizing element 140 to light fluxes parallel to the centraloptical paths of the partial light fluxes. The field lenses 242 and 244arranged before the other liquid-crystal light valves have the samefunction. The green light reflected from the first dichroic mirror 210is reflected again by the second dichroic mirror 212, passes through thefield lens 242, and eventually reaches the liquid-crystal light valve252 for green light. The blue light reflected from the first dichroicmirror 210 is transmitted by the second dichroic mirror 212, passesthrough the relay lens system including the entrance lens 230, the relaylens 232, and the reflecting mirrors 222 and 224, goes through the fieldlens (exit lens) 244, and eventually reaches the liquid-crystal lightvalve 254 for blue light. The relay lens system is used for the bluelight component which has the longer optical path than those of theother colored light components, in order to prevent a decrease inutilization efficiency of light.

The three liquid-crystal light valves 250, 252, and 254 have thefunctions of the light modulation means that respectively modulate thethree colored rays respective to given image information (a given imagesignal) to form images. The cross dichroic prism 260 has the function ofthe colored light combining means that combines the three colored raysand forms a color image. The structure of the dichroic prism 260 isidentical with that described in FIGS. 18 and 19. The cross dichroicprism 260 has a dielectric multi-layered film for reflecting red lightand another dielectric multi-layered film for reflecting blue light thatare arranged in a substantially X shape on an interface of fourright-angle prisms. These dielectric multi-layered films combine thethree colored rays to produce composite light used for projecting acolor image. The composite light generated by the cross dichroic prism260 is output toward the projection lens system 270. The objection lenssystem 270 has the function of the projection optical system at projectsthe composite light on a projection screen 300 to display a color image.

The projection display apparatus 1000 shown in FIG. 5 is characterizedby the stepped reflecting mirror 150. FIG. 8(A) is a front view andFIGS. 8(B) and (C) are plan views respectively showing the structure ofthe stepped reflecting mirror 150. FIGS. 8(B) and (C) are seen from theside of FIG. 8(A). The stepped reflecting mirror 150 has two longstrip-like sub-mirrors 154 mounted on a plane main mirror 152. The twosub-mirrors 154 are bonded horizontally at substantially symmetricalheights from the center of the height of the main mirror 152. Thesemirrors may be total reflection mirrors or cold mirrors that transmitthermal energy. These mirrors may further have the function oftransmitting ultraviolet rays as well as thermal energy. The steppedreflecting mirror 150 having the function of transmitting thermal energyand ultraviolet rays reduces the deterioration of polarizers and otherelements generally included in the liquid-crystal light valves 250, 252,and 254 due to the heat or ultraviolet rays.

FIGS. 9 and 10 show the function of the stepped reflecting mirror 150.FIG. 10 is a cross sectional view in an xy plane including the line A--Aof FIG. 9. Two central optical paths are shown by the solid line and theone-dot chain line in FIGS. 9 and 10. The solid lines represents thecentral optical path of light reflected from the sub-mirror 154, whereasthe one-dot chain line represents the central optical path of lightreflected from the main mirror 152. As clearly understood from thesedrawings, the two optical paths of the partial light fluxes pass throughthe small lenses aligned on the same column (at the same position in thex direction) but existing on different rows (at the different positionsin the y direction) in the lens arrays 120 and 130. As shown in FIG. 9,the optical path shown by the solid line is reflected from the steppedreflecting mirror 150 and shifted in the x direction relative to theoptical path shown by the one-dot chain line.

The stepped reflecting mirror 150 shifts the central optical path oflight reflected from the sub-mirror 154 shown by the solid line relativeto the central optical path of light reflected from the main mirror 152shown by the one-dot chain line. This means that the reflecting mirror150 shifts the partial light fluxes reflected from the sub-mirror 154from the partial light fluxes reflected from the main mirror 152 in thex direction among the partial light fluxes passing through the smalllenses aligned on the same column in the lens arrays 120 and 130. Thisstructure causes these two groups of partial light fluxes to enter thesuperposing lens 160 at different positions in the x direction andthereby have different incident angles on the liquid-crystal light valve252.

The two groups of partial light fluxes entering the liquid-crystal lightvalve 252 at different incident angles are modulated by theliquid-crystal light valve 252 and subsequently pass through the crossdichroic prism 260. Referring to FIG. 9, the central optical path of thepartial light flux reflected from the main mirror 152 and that of thepartial light flux reflected from the sub-mirror 154 have differentincident angles on the cross dichroic prism 260, and pass through thecross dichroic prism 260 at different positions relative to a centralaxis 262 of the cross dichroic prism 260. As discussed previously in thefirst and the second principles, when the central optical paths of thepartial light fluxes pass through the cross dichroic prism 260 atdifferent angles or when the central optical paths of the partial lightfluxes are different in position relative to the central axis 262 of thecross dichroic prism 260, dark lines are formed at different positions.The structure of the embodiment accordingly prevents the dark linesformed by the respective partial light fluxes passing through the Msmall lenses aligned on the same column from being converged on oneplace, thereby making the dark lines sufficiently inconspicuous.

FIG. 11 is an enlarged view showing part of the stepped reflectingmirror 150 and the polarizing element 140 of FIG. 9. The polarizingelement 140 converts the incident light fluxes having random polarizedlight components to s-polarized light fluxes. A distance L between thecentral optical path of the s-polarized light flux output via thepolarization separating film 144 and the λ/2 phase difference layer 146and the central optical path of the s-polarized light flux output viathe polarization separating film 144 and the reflecting film 145 is √2times as long as a distance W between the polarization separating film144 and the reflecting film 145. This relationship between L and W isascribed to the fact that the polarization separating film 144 and thereflecting film 145 are inclined at 45 degrees to the light-enteringsurface. As clearly seen from the drawing, this relationship is commonto the central optical path of the s-polarized light flux shown by thesolid line and the central optical path of the s-polarized light fluxshown by the one-dot chain line.

In this embodiment, a thickness h of the sub-mirror 154 is set to behalf the distance W between the polarization separating film 144 and thereflecting film 145. The stepped reflecting mirror 150 is inclined at 45degrees to the system optical axis. The central optical paths shown bythe solid line and the one-dot chain line are accordingly different inposition in the x direction after the light fluxes are reflected fromthe stepped reflecting mirror 150. Namely four central optical paths arearranged at identical intervals of the distance L/2 in the x direction.

The partial light fluxes entering the liquid-crystal light valve 252 atdifferent incident angles are modulated by the liquid-crystal lightvalve 252 and subsequently passes through the cross dichroic prism 260.Referring again to FIG. 9, the four central optical paths shifted fromone another by the stepped reflecting mirror 150 have different incidentangles when entering the cross dichroic prism 260, and pass through thecross dichroic prism 260 at different positions relative to the centralaxis 262 of the cross dichroic prism 260. As discussed previously in thefirst and the second principles, when the central optical paths of thepartial light fluxes have different incident angles and pass through thecross dichroic prism 260 at different angles or when the central opticalpaths of the partial light fluxes are different in position relative tothe central axis 262 of the cross dichroic prism 260, dark lines areformed at different positions. The structure of the embodimentaccordingly prevents the dark lines formed by the respective partiallight fluxes passing through the M small lenses arranged on the samedirection of columns from being converged on one place, thereby makingthe dark lines sufficiently inconspicuous.

As clearly understood from the description regarding FIG. 9, althoughapplication of the stepped reflecting mirror 150 to the lighting opticalsystem including the integrator optical system makes the darks linesinconspicuous, use of the polarizing element makes the dark lines moreinconspicuous. This is ascribed to the following reason. Application ofthe stepped reflecting mirror 150 to the lighting optical systemincluding the integrator optical system causes the central optical pathsof the partial light fluxes passing through the small lenses aligned onthe same column (at the same position in the x direction) in the lensarrays 120 and 130 to be shifted to two different positions in the xdirection, thereby separating the dark lines into two different places.The polarizing element causes the central optical paths of the partiallight fluxes passing through the small lenses aligned on the same column(at the same position in the x direction) in the lens arrays 120 and 130to be shifted to four different positions in the x direction, therebyseparating the dark lines into four different places.

The thickness h of the sub-mirrors 154 is set to cause a distance l tobe different from the distance L where the distance l is between thecentral optical path of the partial light flux deviated in the zdirection by the stepped reflecting mirror 150 and the central opticalpath of the partial light flux not deviated in the z direction among thepartial light fluxes passing through the small lenses existing on thesame column while the distance L is between the central optical path ofthe s-polarized light flux output from the polarization separating film144 and the λ/2 phase difference layer 146 and the central optical pathof the s-polarized light flux output from the polarization separatingfilm 144 and the reflecting film 145. Especially when the thickness h isset to satisfy l=L/2 as shown in FIG. 11, the separate positions of thedark lines projected on the screen have the maximum distance, so thatthe dark lines are made most inconspicuous.

The position and the width of the two sub-mirrors 154 in the directionof height shown in FIG. 8 are determined so that the sub-mirrors 154 islocated at the position where the light flux emitted from the lightsource 110 has the large intensity of light. The intensity of light ofthe partial light flux passing through the small lens existing within afocal distance f of the concave mirror 114 from the center of the heightof the lens arrays 120 and 130 is greater than the intensities of lightof the partial light fluxes passing through the small lenses at theother heights. It is accordingly effective that the sub-mirrors 154 ofthe stepped reflecting mirror 150 are set to shift the optical axis oflight passing through the area which the partial light flux having thegreater intensity of light is reflected from. The width of thesub-mirrors 154 (the dimension in the direction of height) may be setgreater than that shown in FIG. 8. The dark lines on the projectionscreen are conspicuous when the quantity of light of the dark linesbecomes equal to or less than approximately 95% of the quantity of lightof the other part. The dark lines having the quantity of light over therange of approximately 98 to 97% are not significantly conspicuous. Itis thus preferable that the width of the sub-mirrors 154 is adjusted tocause the quantity of light of the dark lines formed by projecting thecentral axis of the cross dichroic prism 260 to be not less thanapproximately 98% of the quantity of light of the other part.

The stepped reflecting mirror 150 shown in FIG. 8 has the two-stepstructure including the main mirror 152 and the sub-mirrors 154. Amulti-stepped reflecting mirror of three- or more-step structure mayalso be applicable.

B. Second Embodiment

FIG. 12 shows a main part of a projection display apparatus 2000 and itslighting optical system as a second embodiment according to the presentinvention. FIG. 12 corresponds to FIG. 9 of the first embodiment. Thesecond embodiment uses a conventional flat reflecting mirror 156 insteadof the stepped reflecting mirror 150 of the first embodiment andincludes planar transparent members 158 interposed between thepolarizing element 140 and the reflecting mirror 156. The otherconstituents of the second embodiment are identical with those of theprojection display apparatus 1000 of the first embodiment. Thetransparent members 158 can be disposed at any place between the secondlens array 130 and the superposing lens 160, for example, between thereflecting mirror 156 and the superposing lens 160.

Two transparent members 158 are disposed at the height corresponding tothe two sub-mirrors 154 shown in FIG. 8. The dimension of thetransparent members 158 in the direction of height is substantiallyequal to that of the sub-mirrors 154 (FIG. 8) discussed in the firstembodiment. The central axis 262 of the cross dichroic prism 260 extendsin the direction perpendicular to the sheet surface of FIG. 12. Thetransparent members 158 are set rotated about the directioncorresponding to the central axis 262 of the cross dichroic prism 260and inclined from the plane of the lens arrays 120 and 130. Thetransparent members 158 may be sheet glass or sheet-like optical glass.

As is known, the planar transparent members 158 have the function ofshifting the optical paths of the rays slantly entering to substantiallyparallel positions. The two transparent members 158 are set respectivelyat the positions corresponding to the two sub-mirrors 154. The opticalpath of the ray passing through the transparent member 158 is shifted inparallel as shown by the one-dot chain line in FIG. 12. The ray shown bythe solid line, on the other hand, does not pass through the transparentmember 158 and keeps the optical path unchanged.

Both the stepped reflecting mirror 150 of the first embodiment and thetransparent members 158 of the second embodiment have the function ofthe optical path shifting means that shifts the optical path of part ofpartial light fluxes among a plurality of partial light fluxes passingthrough the same column in the lens arrays 120 and 130 from the opticalpath of the other partial light fluxes. These elements and thesuperposing lens 160 have the function of the optical path anglechanging means that causes the incident angle of the optical path ofpart of the partial light fluxes entering the cross dichroic prism 260among a plurality of partial light fluxes passing through the samecolumn in the lens arrays 120 and 130 to be different from the incidentangle of the optical path of the other partial light fluxes. The shiftof the optical path by the optical path shifting means is set at leastto be different from the distance between the two linear polarized lightcomponents separated by the polarizing element 140. In the secondembodiment the shift amount of the optical path can be regulated byadjustment of the refractive index, the angle of inclination, and thethickness of the transparent members 158.

Elements other than the stepped reflecting mirror and the transparentmembers may be used as the optical path shifting means. Different typesof elements may be used in combination as the optical path shiftingmeans.

C. Third Embodiment

FIG. 13 is a front view showing the comparison between the lens arrays120 and 130 of the first embodiment and lens arrays 124 and 134 used ina projection display apparatus 3000 of a third embodiment. The thirdembodiment uses these lens arrays 124 and 134 and includes aconventional flat reflecting mirror instead of the stepped reflectingmirror 150. The projection display apparatus 3000 of the thirdembodiment has the same structure as that of the projection displayapparatus 1000 of the first embodiment, except these elements and amodification of the polarizing element discussed later.

As shown in FIG. 13(B), in the lens arrays 124 and 134 of the thirdembodiment, small lenses on the fourth row and the seventh row among tenrows of small lenses are respectively shifted rightward and leftwardfrom the other rows. The small lenses on the fourth row are shiftedrightward by an amount of deviation d from the other rows, whereas thesmall lenses on the seventh row are shifted leftward by the amount ofdeviation d from the other rows.

The fourth row and the seventh row respectively are located at positionsapart from the center of the lens arrays in the direction of height bythe focal distance f of the concave mirror 114. As discussed previously,the partial light flux passing through this height has the greaterintensity of light than those of the partial light fluxes passingthrough the other heights. Shifting the small lenses on these rowsrightward or leftward varies the incident angle of the partial lightfluxes that enter the cross dichroic prism 260 after passing throughthese small lenses. This state is described in detail with FIG. 14. Inthe drawing of FIG. 14, part of the constituents (for example, apolarizing element 148 discussed later) of the projection displayapparatus 3000 of this embodiment are omitted for the clarity ofexplanation. Only the third row and the fourth row in the second lensarray 134 are illustrated in FIG. 14. As clearly seen from FIG. 14, thepartial light fluxes passing through the small lenses on these rows passthrough the cross dichroic prism 260 at different angles, and cause darklines DLd and DLe to be formed at different positions. This structureaccordingly diverges the positions of the darks lines formed on theprojection screen 300 and makes the dark lines sufficientlyinconspicuous. This result is based on the second principle discussedpreviously.

It is preferable that the amount of deviation d of the small lenses onthe fourth row and the seventh row is set to be approximately one thirdof a width P of each small lens. This causes the small lenses on thefourth row to be shifted from the small lenses on the seventh row andseparates the positions of the dark lines formed on the projectionscreen, thereby making the dark lines sufficiently inconspicuous.

FIG. 15 shows the comparison between the polarizing element 140 used inthe first embodiment and that applicable in the third embodiment. FIG.15(A) is a plan view illustrating the second lens array 130 and thepolarizing element 140 of the first embodiment, and FIG. 15(B) is afront view illustrating the polarizing element 140 of the firstembodiment. Referring to these drawings, the polarization beam splitterarray 141 and the selective phase difference plate 142 of the polarizingelement 140 are arranged in such a manner that the constituents thereof(transparent members and λ/2 phase difference plates) extend in thevertical direction seen from the front.

If the lens arrays 124 and 134 shown in FIG. 13(B) are used, apolarizing element shown in either FIG. 15(C) or FIG. 15(D) isapplicable. A polarizing element 148 shown in FIG. 15(C) has apolarization beam splitter array and a selective phase difference platethat are shifted by an amount of the deviation d at the positionscorresponding to the shifted rows in the lens arrays 124 and 134. Apolarizing element 149 shown in FIG. 15(D), on the other hand, has apolarization beam splitter array and a selective phase difference platethat are arranged to extend in the horizontal direction seen from thefront. The arrangement extending in the horizontal direction as shown inFIG. 15(D) enables the same polarizing element to be applied even whenthe amount of deviation d of the rows in the lens array is varied. Forthat purpose, a sufficiently large width is required for the polarizingelement of FIG. 15(D).

D. Fourth Embodiment

FIG. 16 is a front view showing the comparison between the lens arrays120 and 130 of the first embodiment and lens arrays 126 and 136 used ina fourth embodiment. The fourth embodiment has the same structure asthat of the third embodiment, except that these lens arrays 126 and 136and a polarizing element suitable for the lens arrays are used in thefourth embodiment. The polarizing element applicable in the fourthembodiment may be similar to that of the third embodiment shown in FIG.15 and is thus not specifically described here.

Referring to FIG. 16(B), in the lens arrays 126 and 136 of the fourthembodiment, the respective rows of small lenses are shifted in asuccessive manner. The first, the fourth, the seventh, and the tenthrows are arranged at an identical position, whereas the second, thefifth, and the eighth rows and the third, the sixth, and the ninth rowsare arranged respectively at identical positions. When the position ofthe first row is defined as the reference position, the second, thefifth, and the eighth rows are shifted rightward from the first row byan amount of deviation d. The third, the sixth, and the ninth rows are,on the other hand, shifted leftward from the first row by the amount ofdeviation d.

It is preferable that the amount of deviation d is set to beapproximately one third of the width P of each small lens. This causesonly two fifths of ten rows to be overlapped in the vertical direction(that is, in the direction of columns). As discussed previously, aplurality of small lenses aligned on the same column project the centralaxis of the cross dichroic prism 260 at the same position on theprojection screen to form a dark line. Shifting the rows of the lensarray rightward or leftward to reduce the number of rows overlapping onthe same column in the lens array to be not greater than approximatelytwo fifths makes the dark lines formed on the projection screen 300sufficiently inconspicuous.

It is more preferable that the amount of deviation d is set to beapproximately one quarter of the width P of each small lens. In general,it is preferable that the respective rows are shifted leftward orrightward by the amount of deviation d in the range of approximately onethird to one fifth of the width P of each small lens.

Some variations in the two lens arrays and the polarizing element likethe third and the fourth embodiments enable the dark lines formed byprojecting the central axis of the cross dichroic prism 260 on theprojection screen 300 to be sufficiently inconspicuous.

The invention of making the dark lines inconspicuous is not restrictedto the above embodiments or modes, but there may be many modifications,changes, and alterations without departing from the scope or spirit ofthe main characteristics of the present invention.

The projection display apparatus of the present invention includes: alighting optical system which emits light; three light modulation meanswhich respectively modulate three colored rays based on given imagesignals; colored light combining means which has two dichroic filmsarranged in an X shape and a central axis corresponding to a positionwhere the two dichroic films cross each other, where the colored lightcombining means combines the three colored rays respectively modulatedby the three light modulation means and outputs the composite light in acommon direction; and projection means which projects the compositelight output from the colored light combining means on a projectionsurface. The lighting optical system includes a dividing and superposingoptical system that divides a light flux at least in a predetermineddirection corresponding to the central axis of the colored lightcombining means into a plurality of partial light fluxes of at least onecolumn and superposes the plurality of partial light fluxes on eachlight modulation means. The dividing and superposing optical system isconstructed to shift a position where the central axis of the coloredlight combining means is projected on the projection surface by part ofthe partial light fluxes among the plurality of partial light fluxes onone column, from a position where the central axis is projected by theother partial light fluxes in a direction different from thatcorresponding to the central axis of the colored light combining means.This structure causes part of the partial light fluxes among theplurality of partial light fluxes arranged on one column to project thecentral axis of the colored light combining means as a dark line at adifferent position on the projection surface from the position of a darkline formed by the other partial light fluxes, thus making the darklines formed on the projected image sufficiently inconspicuous.

In the above embodiments, the polarizing element is used to convert theincident light flux to one linear polarized light component. Thepolarizing element may, however, be omitted. Even in this case, theeffect of making the dark lines formed on the projection screeninconspicuous can be attained in the respective embodiments discussedabove.

All the above embodiments regard the transmission-type projectiondisplay apparatuses. The present invention is, however, also applicableto reflection-type projection display apparatuses. The`transmission-type` implies that the light modulation means, such as theliquid-crystal light valve, transmits light, whereas the`reflection-type` implies that the light modulation means reflectslight. In the reflection-type projection display apparatus, the crossdichroic prism is used both as the colored light separation means whichseparates white light into three colored rays of red, green, and blueand as the colored light combining means which recombines the modulatedthree colored rays and emits the composite light in a predetermineddirection. The reflection-type projection display apparatus to which thepresent invention is applied has similar effects to those of thetransmission-type projection display apparatus.

The lighting optical system of the present invention is applicable to avariety of projection display apparatuses. The projection displayapparatus of the present invention may be used to project and displayimages output from a computer or images output from a video cassetterecorder on a screen.

What is claimed is:
 1. A projection display apparatus, comprising:alighting optical system which emits light; colored light separationmeans which separates the light into three colored rays; three lightmodulation means which respectively modulate the three colored raysbased on given image signals; colored light combining means which hastwo dichroic films arranged in an X shape and a central axiscorresponding to a position where the two dichroic films cross eachother, the colored light combining means combining the three coloredrays respectively modulated by the three light modulation means tocomposite light and outputting the composite light in a commondirection; and projection means which projects the composite lightoutput from the colored light combining means on a projection surface,wherein the lighting optical system comprises a dividing and superposingoptical system that divides a light flux into a plurality of partiallight fluxes, which are arranged in a direction of columns substantiallyparallel to the central axis of the colored light combining means and ina direction of rows substantially perpendicular to the central axis ofthe colored light combining means, and superposes the plurality ofpartial light fluxes, and wherein the dividing and superposing opticalsystem is constructed to shift a position where the central axis isprojected on the projection surface by part of the partial light fluxesamong the partial light fluxes on an identical column from a positionwhere the central axis is projected by the other partial light fluxes onthe identical column, the positional shift being in a directiondifferent from a direction corresponding to the central axis.
 2. Aprojection display apparatus in accordance with claim 1, wherein thedividing and superposing optical system comprises:light flux dividingmeans which divides the light flux into the plurality of partial lightfluxes; and incident angle changing means that causes the part of thepartial light fluxes among the partial light fluxes on the identicalcolumn to enter the colored light combining means at an incident angledifferent from that of the other partial light fluxes.
 3. A projectiondisplay apparatus in accordance with claim 2, wherein the light fluxdividing means comprises at least one lens array having a plurality ofsmall lenses arranged in the directions of columns and rows, andtheincident angle changing means comprises a stepped reflecting mirrorhaving a step part on a reflecting surface thereof.
 4. A projectiondisplay apparatus in accordance with claim 2, wherein the light fluxdividing means comprises at least one lens array having a plurality ofsmall lenses arranged in the directions of columns and rows, andtheincident angle changing means comprises a transparent member arranged tobe inclined relative to a surface of the lens array.
 5. A projectiondisplay apparatus, comprising:a lighting optical system which emitslight; colored light separation means which separates the light intothree colored rays; three light modulation means which respectivelymodulate the three colored rays based on given image signals; coloredlight combining means which has two dichroic films arranged in an Xshape and a central axis corresponding to a position where the twodichroic films cross each other, the colored light combining meanscombining the three colored rays respectively modulated by the threelight modulation means to composite light and outputting the compositelight in a common direction; and projection means which projects thecomposite light output from the colored light combining means on aprojection surface, wherein the lighting optical system comprises:afirst lens array having a plurality of small lenses that divide a lightflux emitted from a light source into a plurality of partial lightfluxes; a second lens array having a plurality of small lenses thatrespectively correspond to the plurality of small lenses of the firstlens array; and optical path shifting means which shifts an optical pathof part of the partial light fluxes among a plurality of partial lightfluxes passing through the plurality of small lenses arranged in apredetermined direction corresponding to the central axis of the coloredlight combining means from an optical path of the other partial lightfluxes among the plurality of partial light fluxes.
 6. A projectiondisplay apparatus in accordance with claim 5, wherein the optical pathshifting means comprises:means which shifts the optical path of thepartial light fluxes passing through positions respectively apart froman optical axis of the light source by a specified distance in thepredetermined direction from the optical path of the partial lightfluxes passing through the other positions.
 7. A projection displayapparatus in accordance with claim 6, wherein the light source comprisesa light-source lamp and a concave mirror that reflects light emittedfrom the light-source lamp, andthe specified distance is substantiallyequal to a focal distance of the concave mirror.
 8. A projection displayapparatus in accordance with claim 5, wherein the optical path shiftingmeans comprises a stepped reflecting mirror having a step part on areflecting surface thereof.
 9. A projection display apparatus inaccordance with claim 8, wherein the step part of the stepped reflectingmirror is arranged to extend in a direction perpendicular to thepredetermined direction.
 10. A projection display apparatus inaccordance with claim 8, wherein the stepped reflecting mirror has afirst reflecting surface and a second reflecting surface of differentheights, the second reflecting surface being arranged at two differentpositions respectively apart from an optical axis of the light source bya specified distance in the predetermined direction corresponding to thecentral axis of the colored light combining means.
 11. A projectiondisplay apparatus in accordance with claim 5, wherein the optical pathshifting means comprises a transparent member arranged to be inclinedrelative to a surface of the second lens array.
 12. A projection displayapparatus in accordance with claim 5, wherein the lighting opticalsystem further comprises:a polarizing element disposed at a positionbetween the second lens array and the optical path shifting means,wherein the polarizing element comprises:a polarization beam splitterarray which has plural sets of a polarization separating film and areflecting film that are parallel to each other, the polarization beamsplitter array separating each of the plurality of partial light fluxespassing through the plurality of small lenses of the second lens arrayinto two types of linear polarized light components; and a polarizerwhich equalizes polarizing directions of the two types of linearpolarized light components separated by the polarization beam splitterarray, and wherein the optical path shifting means shifts part ofoptical paths of the two types of linear polarized light components,which pass through the plurality of small lenses arranged in thepredetermined direction corresponding to the central axis of the coloredlight combining means and are separated by the polarization beamsplitter array, from the other optical paths.
 13. A projection displayapparatus in accordance with claim 12, wherein an amount of shift bywhich the part of the optical paths of the two types of linear polarizedlight components are shifted from the other optical paths by the opticalpath shifting means is approximately half a distance between adjoiningoptical paths of the two types of linear polarized light components. 14.A projection display apparatus in accordance with claim 5, theprojection display apparatus further comprising:a superposing opticalsystem which superposes a plurality of partial light fluxes passingthrough the first lens array and the second lens array to illuminate thethree light modulation means, wherein the optical path shifting means isdisposed between the second lens array and the superposing opticalsystem.
 15. A projection display apparatus, comprising:a lightingoptical system which emits light; colored light separation means whichseparates the light into three colored rays; three light modulationmeans which respectively modulate the three colored rays based on givenimage signals; colored light combining means which has two dichroicfilms arranged in an X shape and a central axis corresponding to aposition where the two dichroic films cross each other, the coloredlight combining means combining the three colored rays respectivelymodulated by the three light modulation means to composite light andoutputting the composite light in a common direction; and projectionmeans which projects the composite light output from the colored lightcombining means on a projection surface, wherein the lighting opticalsystem comprises:a first lens array having a plurality of small lensesthat divide a light flux emitted from a light source into a plurality ofpartial light fluxes; and a second lens array having a plurality ofsmall lenses that respectively correspond to the plurality of smalllenses of the first lens array, each of the first lens array and thesecond lens array being divided in a direction of rows perpendicular toa direction corresponding to the central axis of the colored lightcombining means into a plurality of rows each having a plurality ofsmall lenses, wherein rows located respectively apart from an opticalpath of the light source by a specified distance in the directioncorresponding to the central axis of the colored light combining meansare arranged at positions shifted from the other rows by a fixed amountof shift.
 16. A projection display apparatus in accordance with claim15, wherein the light source comprises a light-source lamp and a concavemirror that reflects light emitted from the light-source lamp, andthespecified distance is substantially equal to a focal distance of theconcave mirror.
 17. A projection display apparatus, comprising:alighting optical system which emits light; colored light separationmeans which separates the light into three colored rays; three lightmodulation means which respectively modulate the three colored raysbased on given image signals; colored light combining means which hastwo dichroic films arranged in an X shape and a central axiscorresponding to a position where the two dichroic films cross eachother, the colored light combining means combining the three coloredrays respectively modulated by the three light modulation means tocomposite light and outputting the composite light in a commondirection; and projection means which projects the composite lightoutput from the colored light combining means on a projection surface,wherein the lighting optical system comprises:a first lens array havinga plurality of small lenses that divide a light flux emitted from alight source into a plurality of partial light fluxes; and a second lensarray having a plurality of small lenses that respectively correspond tothe plurality of small lenses of the first lens array, each of the firstlens array and the second lens array being divided in a direction ofrows perpendicular to a direction corresponding to the central axis ofthe colored light combining means into a plurality of rows each having aplurality of small lenses, wherein at least part of the rows among theplurality of rows are arranged at a position shifted from the otherrows, and a number of rows whose small lenses are arranged at identicalpositions in a direction perpendicular to the direction of rows is setto be not greater than two fifths of a total number of the plurality ofrows.
 18. A projection display apparatus in accordance with claim 17,wherein the plurality of rows in the first lens array and the secondlens array are shifted from one another by a fixed amount of shift. 19.A lighting optical system for emitting light for use in a projectiondisplay apparatus comprising: colored light separation means whichseparates the light into three colored rays; three light modulationmeans which respectively modulate the three colored rays based on givenimage signals; colored light combining means which has two dichroicfilms arranged in an X shape and a central axis corresponding to aposition where the two dichroic films cross each other, the coloredlight combining means combining the three colored rays respectivelymodulated by the three light modulation means to composite light andoutputting the composite light in a common direction; and projectionmeans which projects the composite light output from the colored lightcombining means on a projection surface, the lighting optical systemcomprising:a dividing and superposing optical system that divides alight flux into a plurality of partial light fluxes, which are arrangedin a direction of columns substantially parallel to the central axis ofthe colored light combining means and in a direction of rowssubstantially perpendicular to the central axis of the colored lightcombining means, and superposes the plurality of partial light fluxes,wherein the dividing and superposing optical system is constructed toshift a position where the central axis is projected on the projectionsurface by part of the partial light fluxes among the partial lightfluxes on an identical column from a position where the central axis isprojected by the other partial light fluxes on the identical column, thepositional shift being in a direction different from a directioncorresponding to the central axis.
 20. A lighting optical system inaccordance with claim 19, wherein the dividing and superposing opticalsystem comprises:light flux dividing means which divides the light fluxinto the plurality of partial light fluxes; and incident angle changingmeans that causes the part of the partial light fluxes among the partiallight fluxes on the identical column to enter the colored lightcombining means at an incident angle different from that of the otherpartial light fluxes.
 21. A lighting optical system in accordance withclaim 20, wherein the light flux dividing means comprises at least onelens array having a plurality of small lenses arranged in the directionsof columns and rows, andthe incident angle changing means comprises astepped reflecting mirror having a step part on a reflecting surfacethereof.
 22. A lighting optical system in accordance with claim 20,wherein the light flux dividing means comprises at least one lens arrayhaving a plurality of small lenses arranged in the directions of columnsand rows, andthe incident angle changing means comprises a transparentmember arranged to be inclined relative to a surface of the lens array.23. A lighting optical system that emits light, the lighting opticalsystem comprising:a first lens array having a plurality of small lensesthat divide a light flux emitted from a light source into a plurality ofpartial light fluxes; a second lens array having a plurality of smalllenses that respectively correspond to the plurality of small lenses ofthe first lens array; and optical path shifting means which shifts anoptical path of part of the partial light fluxes among a plurality ofpartial light fluxes passing through the plurality of small lensesarranged in a predetermined direction from an optical path of the otherpartial light fluxes among the plurality of partial light fluxes.
 24. Alighting optical system in accordance with claim 23, wherein the opticalpath shifting means comprises:means which shifts the optical path of thepartial light fluxes passing through positions respectively apart froman optical axis of the light source by a specified distance in thepredetermined direction from the optical path of the partial lightfluxes passing through the other positions.
 25. A lighting opticalsystem in accordance with claim 24, wherein the light source comprises alight-source lamp and a concave mirror that reflects light emitted fromthe light-source lamp, andthe specified distance is substantially equalto a focal distance of the concave mirror.
 26. A lighting optical systemin accordance with claim 23, wherein the optical path shifting meanscomprises a stepped reflecting mirror having a step part on a reflectingsurface thereof.
 27. A lighting optical system in accordance with claim26, wherein the step part of the stepped reflecting mirror is arrangedto extend in a direction perpendicular to the predetermined direction.28. A lighting optical system in accordance with claim 26, wherein thestepped reflecting mirror has a first reflecting surface and a secondreflecting surface of different heights, the second reflecting surfacebeing arranged at two different positions respectively apart from anoptical axis of the light source by a specified distance in thepredetermined direction.
 29. A lighting optical system in accordancewith claim 23, wherein the optical path shifting means comprises atransparent member arranged to be inclined relative to a surface of thesecond lens array.
 30. A lighting optical system in accordance withclaim 23, the lighting optical system further comprising:a polarizingelement disposed at a position between the second lens array and theoptical path shifting means, wherein the polarizing element comprises:apolarization beam splitter array which has plural sets of a polarizationseparating film and a reflecting film that are parallel to each other,the polarization beam splitter array separating each of the plurality ofpartial light fluxes passing through the plurality of small lenses ofthe second lens array into two types of linear polarized lightcomponents; and a polarizer which equalizes polarizing directions of thetwo types of linear polarized light components separated by thepolarization beam splitter array, and wherein the optical path shiftingmeans shifts part of optical paths of the two types of linear polarizedlight components, which pass through the plurality of small lensesarranged in the predetermined direction and are separated by thepolarization beam splitter array, from the other optical paths.
 31. Alighting optical system in accordance with claim 30, wherein an amountof shift by which the part of the optical paths of the two types oflinear polarized light components are shifted from the other opticalpaths by the optical path shifting means is approximately half adistance between adjoining optical paths of the two types of linearpolarized light components.
 32. A lighting optical system in accordancewith claim 23, the lighting optical system further comprising:asuperposing optical system which superposes a plurality of partial lightfluxes passing through the first lens array and the second lens array toilluminate the three light modulation means, wherein the optical pathshifting means is disposed between the second lens array and thesuperposing optical system.
 33. A lighting optical system that emitslight, the lighting optical system comprising:a first lens array havinga plurality of small lenses that divide a light flux emitted from alight source into a plurality of partial light fluxes; and a second lensarray having a plurality of small lenses that respectively correspond tothe plurality of small lenses of the first lens array, each of the firstlens array and the second lens array being divided in a direction ofrows perpendicular to a predetermined direction into a plurality of rowseach having a plurality of small lenses, wherein rows locatedrespectively apart from an optical path of the light source by aspecified distance in the predetermined direction are arranged atpositions shifted from the other rows by a fixed amount of shift.
 34. Alighting optical system in accordance with claim 33, wherein the lightsource comprises a light-source lamp and a concave mirror that reflectslight emitted from the light-source lamp, andthe specified distance issubstantially equal to a focal distance of the concave mirror.
 35. Alighting optical system that emits light, the lighting optical systemcomprising:a first lens array having a plurality of small lenses thatdivide a light flux emitted from a light source into a plurality ofpartial light fluxes; and a second lens array having a plurality ofsmall lenses that respectively correspond to the plurality of smalllenses of the first lens array, each of the first lens array and thesecond lens array being divided in a direction of rows perpendicular toa predetermined direction into a plurality of rows each having aplurality of small lenses, wherein at least part of the rows among theplurality of rows are arranged at a position shifted from the otherrows, and a number of rows whose small lenses are arranged at identicalpositions in a direction perpendicular to the direction of rows is setto be not greater than two fifths of a total number of the plurality ofrows.
 36. A lighting optical system in accordance with claim 35, whereinthe plurality of rows in the first lens array and the second lens arrayare shifted from one another by a fixed amount of shift.